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92-434: The total length of the tunnel, including on- and off-ramps, is 1682 metres. The covered part is 1039 metres long. The deepest point of the tunnel lies 20.32 metres below sea-level. The tunnel was built of sections of rectangular concrete constructions of 24.8 x 8.75 metres, subdivided into two tubes for automobile traffic and in between tubes for cables and pipes. Ventilators, located in two ventilation buildings on

184-412: A bitumen binder, which is frequently used for road surfaces , and polymer concretes that use polymers as a binder. Concrete is distinct from mortar . Whereas concrete is itself a building material, mortar is a bonding agent that typically holds bricks , tiles and other masonry units together. Grout is another material associated with concrete and cement. It does not contain coarse aggregates and

276-433: A French structural and civil engineer . Concrete components or structures are compressed by tendon cables during, or after, their fabrication in order to strengthen them against tensile forces developing when put in service. Freyssinet patented the technique on 2 October 1928. Concrete is an artificial composite material , comprising a matrix of cementitious binder (typically Portland cement paste or asphalt ) and

368-573: A Portland stone façade to complete its stripped Classical design. After the Second World War (1939–1945), the bombed out centres of many English towns and cities, such as Plymouth , Bristol , Coventry and London were reconstructed using vast facades of Portland stone. Many of the buildings surrounding the flagship Parkinson Building at the University of Leeds are clad in Portland stone, including

460-452: A cementitious material forms a cement paste by the process of hydration. The cement paste glues the aggregate together, fills voids within it, and makes it flow more freely. As stated by Abrams' law , a lower water-to-cement ratio yields a stronger, more durable concrete, whereas more water gives a freer-flowing concrete with a higher slump . The hydration of cement involves many concurrent reactions. The process involves polymerization ,

552-400: A concrete component—and become a part of the binder for the aggregate. Fly ash and slag can enhance some properties of concrete such as fresh properties and durability. Alternatively, other materials can also be used as a concrete binder: the most prevalent substitute is asphalt , which is used as the binder in asphalt concrete . Admixtures are added to modify the cure rate or properties of

644-434: A dispersed phase or "filler" of aggregate (typically a rocky material, loose stones, and sand). The binder "glues" the filler together to form a synthetic conglomerate . Many types of concrete are available, determined by the formulations of binders and the types of aggregate used to suit the application of the engineered material. These variables determine strength and density, as well as chemical and thermal resistance of

736-426: A gas. Calcium and bicarbonate ions within the water are then able to combine, to form calcium carbonate (CaCO 3 ) as a precipitate. The process of limescale build up in a kettle in hard-water areas is similar. Calcium carbonate is the principal constituent of most limestones. Billions of minute crystals of precipitated calcium carbonate (called calcite ) accumulated forming lime mud (called micrite ) which covered

828-452: A greater degree of fracture resistance even in seismically active environments. Roman concrete is significantly more resistant to erosion by seawater than modern concrete; it used pyroclastic materials which react with seawater to form Al- tobermorite crystals over time. The use of hot mixing and the presence of lime clasts are thought to give the concrete a self-healing ability, where cracks that form become filled with calcite that prevents

920-546: A key event in the history of architecture termed the Roman architectural revolution , freed Roman construction from the restrictions of stone and brick materials. It enabled revolutionary new designs in terms of both structural complexity and dimension. The Colosseum in Rome was built largely of concrete, and the Pantheon has the world's largest unreinforced concrete dome. Concrete, as

1012-415: A large aggregate that is too large for the size of the formwork, or which has too few smaller aggregate grades to serve to fill the gaps between the larger grades, or using too little or too much sand for the same reason, or using too little water, or too much cement, or even using jagged crushed stone instead of smoother round aggregate such as pebbles. Any combination of these factors and others may result in

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1104-461: A large type of industrial facility called a concrete plant , or often a batch plant. The usual method of placement is casting in formwork , which holds the mix in shape until it has set enough to hold its shape unaided. Concrete plants come in two main types, ready-mix plants and central mix plants. A ready-mix plant blends all of the solid ingredients, while a central mix does the same but adds water. A central-mix plant offers more precise control of

1196-493: A machine. Slots are cut into the top, bottom, sides and middle of the stone. A flat steel pillow is inserted into the middle cut and slowly inflated with water. The stones are gently broken off at the back without placing any stress on the resulting blocks. This method of extraction is significantly more expensive than blasting, but results in a higher yield thereby saving valuable reserves for future generations. The environmental benefits are substantial as mining significantly reduces

1288-592: A mix which is too harsh, i.e., which does not flow or spread out smoothly, is difficult to get into the formwork, and which is difficult to surface finish. Portland stone Vale of Wardour : Tisbury Member, Wockley Member, Chilmark Member Portland stone is a limestone geological formation (formally named the Portland Stone Formation ) dating to the Tithonian age of the Late Jurassic that

1380-469: A mixture of calcium silicates ( alite , belite ), aluminates and ferrites —compounds, which will react with water. Portland cement and similar materials are made by heating limestone (a source of calcium) with clay or shale (a source of silicon, aluminium and iron) and grinding this product (called clinker ) with a source of sulfate (most commonly gypsum ). Cement kilns are extremely large, complex, and inherently dusty industrial installations. Of

1472-405: A number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted. The size distribution of the aggregate determines how much binder is required. Aggregate with a very even size distribution has the biggest gaps whereas adding aggregate with smaller particles tends to fill these gaps. The binder must fill the gaps between the aggregate as well as paste

1564-647: A popularity amongst masons and architects that has endured ever since. The East side of Buckingham Palace , the official London residence of King Charles III , including the balcony, was faced with Portland stone, first in 1854 and again in 1913. The Victoria Memorial (unveiled 1911) is also made of it. Inigo Jones (1573–1652) used Portland stone to build the Banqueting Hall in Whitehall in 1620. Sir Christopher Wren used nearly one million cubic feet to rebuild St. Paul's Cathedral and many other minor churches after

1656-424: A semi-liquid slurry (paste) that can be shaped, typically by pouring it into a form. The concrete solidifies and hardens through a chemical process called hydration . The water reacts with the cement, which bonds the other components together, creating a robust, stone-like material. Other cementitious materials, such as fly ash and slag cement , are sometimes added—either pre-blended with the cement or directly as

1748-493: A simple, fast way of getting a basic idea of the properties of the finished concrete without having to perform testing in advance. Various governing bodies (such as British Standards ) define nominal mix ratios into a number of grades, usually ranging from lower compressive strength to higher compressive strength. The grades usually indicate the 28-day cure strength. Thorough mixing is essential to produce uniform, high-quality concrete. Separate paste mixing has shown that

1840-461: A small empire in the regions of southern Syria and northern Jordan from the 4th century BC. They discovered the advantages of hydraulic lime , with some self-cementing properties, by 700 BC. They built kilns to supply mortar for the construction of rubble masonry houses, concrete floors, and underground waterproof cisterns . They kept the cisterns secret as these enabled the Nabataeans to thrive in

1932-451: Is Rufus Castle at Church Ope Cove, Portland. The original structure was probably built around 1080, rebuilt around 1259 and rebuilt yet again around 1450, which is the likely date of the walls seen today. The first known Portland stone quarries were situated on the northeastern coast of the Isle, close to Rufus Castle, where huge landslips made the stone more easily accessible, and the proximity of

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2024-484: Is exothermic , which means ambient temperature plays a significant role in how long it takes concrete to set. Often, additives (such as pozzolans or superplasticizers ) are included in the mixture to improve the physical properties of the wet mix, delay or accelerate the curing time, or otherwise change the finished material. Most concrete is poured with reinforcing materials (such as steel rebar ) embedded to provide tensile strength , yielding reinforced concrete . In

2116-597: Is quarried on the Isle of Portland in Dorset , England. The quarries are cut in beds of white-grey limestone separated by chert beds. It has been used extensively as a building stone throughout the British Isles , notably in major public buildings in London such as St Paul's Cathedral and Buckingham Palace . Portland stone is also exported to many countries, being used for example at

2208-405: Is a composite material composed of aggregate bonded together with a fluid cement that cures to a solid over time. Concrete is the second-most-used substance in the world after water , and is the most widely used building material. Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined. When aggregate is mixed with dry Portland cement and water ,

2300-721: Is also built with Portland stone, as are the public buildings in Cardiff's civic centre. Architect Charles Holden significantly used the stone in his major commissions of the 1920s and 1930s, including Senate House and 55 Broadway , the home of the London Underground . The 1929 steel framed building (one of the first erected in the United Kingdom) of the London School of Hygiene & Tropical Medicine , based in Keppel Street, has

2392-462: Is also worth noting that stone tends to split much more easily parallel to bedding planes (called graining) than perpendicular to them (called cutting). In 1999, Italian stone cutting equipment, originally designed for use in Tuscany 's marble quarries was imported by Albion Stone and applied to the extraction of Portland stone. This new technology eliminated the need for blasting, significantly improved

2484-468: Is flat and had been covered with cement". "The floors were cement, in some places hard, but, by long exposure, broken, and now crumbling under the feet." "But throughout the wall was solid, and consisting of large stones imbedded in mortar, almost as hard as rock." Small-scale production of concrete-like materials was pioneered by the Nabatean traders who occupied and controlled a series of oases and developed

2576-568: Is privately owned by Portland Stone Firms. Open cast quarrying provides quicker extraction of raw block dimension stone whilst maintaining its integrity. The majority of buildings in London today use Portland which has been quarried using the same methods over the last 60 years. Broadcroft Quarry is located on the eastern side of the island and is a part of the open cast quarries used for St Paul's Cathedral. Privately owned by Portland Stone Firms Limited there are over 20 years of reserves left and still being actively quarried. The coastal strip toward

2668-452: Is similar to the way in which a snowball grows in size as it is rolled around in the snow. Over time, countless billions of these balls, known as " ooids " or "ooliths" (from the Greek for "egg-shaped" or "egg-stone"), became partially cemented together (or lithified) by more calcite, to form the oolitic limestone that is called Portland stone. The degree of cementation in Portland stone is such that

2760-559: Is then blended with aggregates and any remaining batch water and final mixing is completed in conventional concrete mixing equipment. Workability is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (pouring, pumping, spreading, tamping, vibration) and without reducing the concrete's quality. Workability depends on water content, aggregate (shape and size distribution), cementitious content and age (level of hydration ) and can be modified by adding chemical admixtures, like superplasticizer. Raising

2852-562: Is usually either pourable or thixotropic , and is used to fill gaps between masonry components or coarse aggregate which has already been put in place. Some methods of concrete manufacture and repair involve pumping grout into the gaps to make up a solid mass in situ . The word concrete comes from the Latin word " concretus " (meaning compact or condensed), the perfect passive participle of " concrescere ", from " con -" (together) and " crescere " (to grow). Concrete floors were found in

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2944-399: Is usually reinforced with materials that are strong in tension, typically steel rebar . The mix design depends on the type of structure being built, how the concrete is mixed and delivered, and how it is placed to form the structure. Portland cement is the most common type of cement in general usage. It is a basic ingredient of concrete, mortar , and many plasters . It consists of

3036-514: The Great Fire of London in 1666. All of the stone used by Wren was transported by sailing barge from Portland to the centre of London via the sea and then up the Thames. Wren's widespread use of Portland stone firmly established it as London's "local stone" and as one of the best-loved British building stones. Other famous London buildings constructed of Portland stone are The British Museum (1753) with

3128-878: The Michael Sadler Building, the Chemistry and Engineering buildings and the new Laidlaw Library. Oxford typically uses oolitic limestone in its buildings, and the Ashmolean Museum has been refurbished using a large amount of Portland stone. Portland stone has also been used across the world. Examples include the UN building in New York, the Casino Kursaal in Belgium and the Auckland War Memorial Museum . Most of

3220-621: The Prins Hendrikkade in the south, where it is reduced to two lanes, one in each direction. The IJtunnel is a class D tunnel under the ADR treaty . The classification means that no one may use the tunnel to transport dangerous goods that may cause a large explosion, or a large toxic release, or a large fire. The tunnel is also an entry point to Amsterdam's low emission zone , and there is a height limit of 4 meters. Pedestrians, agricultural vehicles, bicycles and mopeds are generally not allowed to use

3312-514: The United Nations headquarters in New York City. Portland stone formed in a marine environment, on the floor of a shallow, warm, sub-tropical sea probably near land (as evidenced by fossilised driftwood, which is not uncommon). When seawater is warmed by the sun, its capacity to hold dissolved gas is reduced; consequently, dissolved carbon dioxide (CO 2 ) is released into the atmosphere as

3404-480: The construction industry , whose demand is ever growing with greater impacts on raw material extraction, waste generation and landfill practices. Concrete production is the process of mixing together the various ingredients—water, aggregate, cement, and any additives—to produce concrete. Concrete production is time-sensitive. Once the ingredients are mixed, workers must put the concrete in place before it hardens. In modern usage, most concrete production takes place in

3496-640: The "New Build (Modern Non-Load-bearing Stone) Award" in the 2006 Natural Stone Awards. Portland stone has been designated by the International Union of Geological Sciences as a Global Heritage Stone Resource . Following the First World War, Sir Edwin Lutyens used Portland stone (quarried from the bottom of Wakeham) to construct the Cenotaph in London's Whitehall. Erected in 1920, The Cenotaph commemorates

3588-571: The 1930s. Manchester buildings with Portland stone exterior include 100 King Street (1935), Arkwright House (1937), St. James Buildings (1912), Manchester Central Library (1934), Kendal Milne (1939) and Sunlight House (1932). Two of Liverpool's Three Graces , the Cunard Building and the Port of Liverpool Building , are clad in Portland stone which surrounds their reinforced concrete frames. The Nottingham Council House , completed in 1929,

3680-516: The IJtunnel. However, the ban on pedestrians, bicycles and mopeds may be temporarily lifted if public transport and ferry services across the IJ are suspended: such a situation occurred in 1993, 1997, 2005 and 28 May 2019. There was also a special open day on 26 October 1968, to mark the opening of the tunnel. The tunnel is also used by runners during the annual Dam tot Damloop . Concrete Concrete

3772-504: The Romans knew it, was a new and revolutionary material. Laid in the shape of arches , vaults and domes , it quickly hardened into a rigid mass, free from many of the internal thrusts and strains that troubled the builders of similar structures in stone or brick. Modern tests show that opus caementicium had as much compressive strength as modern Portland-cement concrete (c. 200 kg/cm  [20 MPa; 2,800 psi]). However, due to

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3864-560: The School of Ocean and Earth Sciences at Southampton University completed a detailed geological survey of Withies Croft Quarry before the Portland Beds were quarried by Albion Stone plc. Stone has been quarried on Portland since Roman times and was being shipped to London in the 14th century. Extraction as an industry began in the early 17th century, with shipments to London for Inigo Jones ' Banqueting House . Wren 's choice of Portland for

3956-639: The absence of reinforcement, its tensile strength was far lower than modern reinforced concrete , and its mode of application also differed: Modern structural concrete differs from Roman concrete in two important details. First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering together with the placement of aggregate, which, in Roman practice, often consisted of rubble . Second, integral reinforcing steel gives modern concrete assemblies great strength in tension, whereas Roman concrete could depend only upon

4048-501: The banks of the IJ, blow clean air into the traffic areas via tubes under the surface of the road and openings in the tunnel walls, and suck polluted air out. At the entrance on the north side there are sun-blocking lattices over the road. These lattices are missing on the south side, where the Nemobuilding is built on top of the tunnel. The traffic in the tunnel is monitored by 22 closed-circuit cameras . A heating system prevents

4140-506: The building of Chelsea Barracks , Wilkins Terrace at UCL University College London , St James's Market Haymarket, London and Green Park tube station . Portland stone is prevalent in Manchester despite the historical preferred use of hard-wearing materials, such as Burmantofts and sandstone to resist the harsh industrial environment. Portland stone was mostly used in Manchester during

4232-526: The concrete at the time of batching/mixing. (See § Production below.) The common types of admixtures are as follows: Inorganic materials that have pozzolanic or latent hydraulic properties, these very fine-grained materials are added to the concrete mix to improve the properties of concrete (mineral admixtures), or as a replacement for Portland cement (blended cements). Products which incorporate limestone , fly ash , blast furnace slag , and other useful materials with pozzolanic properties into

4324-399: The concrete can cause the initially placed material to begin to set before the next batch is added on top. This creates a horizontal plane of weakness called a cold joint between the two batches. Once the mix is where it should be, the curing process must be controlled to ensure that the concrete attains the desired attributes. During concrete preparation, various technical details may affect

4416-461: The concrete quality. Central mix plants must be close to the work site where the concrete will be used, since hydration begins at the plant. A concrete plant consists of large hoppers for storage of various ingredients like cement, storage for bulk ingredients like aggregate and water, mechanisms for the addition of various additives and amendments, machinery to accurately weigh, move, and mix some or all of those ingredients, and facilities to dispense

4508-477: The crack from spreading. The widespread use of concrete in many Roman structures ensured that many survive to the present day. The Baths of Caracalla in Rome are just one example. Many Roman aqueducts and bridges, such as the magnificent Pont du Gard in southern France, have masonry cladding on a concrete core, as does the dome of the Pantheon . After the Roman Empire, the use of burned lime and pozzolana

4600-554: The desert. Some of these structures survive to this day. In the Ancient Egyptian and later Roman eras, builders discovered that adding volcanic ash to lime allowed the mix to set underwater. They discovered the pozzolanic reaction . The Romans used concrete extensively from 300 BC to AD 476. During the Roman Empire, Roman concrete (or opus caementicium ) was made from quicklime , pozzolana and an aggregate of pumice . Its widespread use in many Roman structures ,

4692-483: The extreme southern end of the quarry and the High Wall Extraction on the eastern and south east boundaries. High Wall Extraction is a series of small mines that extract otherwise wasted stone that sits between the final faces of the quarry and the actual boundary of the site. Stonehills Mine is the first completely new mine on Portland (not a mine as an extension from an existing quarry). Albion Stone Plc began

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4784-431: The finished product. Construction aggregates consist of large chunks of material in a concrete mix, generally a coarse gravel or crushed rocks such as limestone , or granite , along with finer materials such as sand . Cement paste, most commonly made of Portland cement , is the most prevalent kind of concrete binder. For cementitious binders, water is mixed with the dry cement powder and aggregate, which produces

4876-436: The forces necessary to loosen the stone to the point where it can be easily removed using large wheeled loaders . Splitting stone, using pneumatic drills is arduous work and so wire-saws have been introduced into the quarries, replacing much of the plug and feather cutting. Mining in Portland is done by using a room and pillar method. The mine is advanced by extracting the stone using an abrasive tool chain cutter mounted on

4968-446: The forming of ice on the surface of the road, and a computer regulates the intensity of light at the beginning and the end of the tunnel, so that a gradual transition from tunnel light to daylight takes place. The route through the IJtunnel is an urban avenue, formed out of two divided tunnels, each with two lanes of traffic. This four-lane road continues to the A10 in the north and to

5060-403: The impact on the environment and local residents. Jordan's Mine is currently the biggest mine on Portland. Bowers Quarry has been operational since the late 18th century. It has been leased from The Crown Estate since 1979, and in 2002 it became the site of the first Portland stone mine by Albion Stone PLC. Extraction from this site is now completely underground, with the original Bowers Mine in

5152-455: The impact on wildlife and the local community with reduced noise and dust. Portland's freestone has almost certainly been used as a building material since Roman times. The many well crafted Roman sarcophagi (stone coffins and matching lids, hewn from single large blocks of Portland stone) that have been unearthed locally over the years, testify to the skill of their makers. The earliest known building to be constructed using Portland stone

5244-754: The important civic and administrative buildings which survive from 18th and 19th century Dublin , Ireland, known then as "the second city of the Empire", are of Portland stone, including City Hall (1779), the Houses of Parliament (1767), the Custom House (1791), the National Gallery (1864) and the General Post Office (1818). More recent projects include the BBC Broadcasting House in London, which won

5336-554: The interlinking of the silicates and aluminate components as well as their bonding to sand and gravel particles to form a solid mass. One illustrative conversion is the hydration of tricalcium silicate: The hydration (curing) of cement is irreversible. Fine and coarse aggregates make up the bulk of a concrete mixture. Sand , natural gravel, and crushed stone are used mainly for this purpose. Recycled aggregates (from construction, demolition, and excavation waste) are increasingly used as partial replacements for natural aggregates, while

5428-411: The island, which also includes Fancy Beach. The quarry has been worked since the late 19th century. Albion Stone leases the southern section from The Crown Estate and purchased the northern part of the site in 2006. The majority of the southern reserves lie under the grounds of the local cricket club. To avoid disturbing the site at surface level, the company has applied and received permission to extract

5520-409: The last 80 years and is one of three privately owned quarries by Portland Stone Firms Ltd, the largest landholder on the island. The quarry is nearing the end of its life and will be regenerated as a holiday caravan park to boost local tourism on the island. Perryfield Quarry is found towards the middle of the island and being actively open cast quarried. There are over 20 years of reserves left which

5612-406: The making of mortar. In an English translation from 1397, it reads "lyme ... is a stone brent; by medlynge thereof with sonde and water sement is made". From the 14th century, the quality of mortar was again excellent, but only from the 17th century was pozzolana commonly added. The Canal du Midi was built using concrete in 1670. Perhaps the greatest step forward in the modern use of concrete

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5704-531: The material. Mineral admixtures use recycled materials as concrete ingredients. Conspicuous materials include fly ash , a by-product of coal-fired power plants ; ground granulated blast furnace slag , a by-product of steelmaking ; and silica fume , a by-product of industrial electric arc furnaces . Structures employing Portland cement concrete usually include steel reinforcement because this type of concrete can be formulated with high compressive strength , but always has lower tensile strength . Therefore, it

5796-564: The millions of people killed in this and subsequent conflicts. The RAF Bomber Command Memorial in London's Green Park commemorates the 55,573 crew members of the RAF's Bomber Command who were killed between 1939 and 1945. The gravestones for British personnel killed in the First and Second World Wars were made out of Portland stone. The Commonwealth War Graves Commission use Portland Limestone supplier Albion Stone's Portland Basebed. Portland stone

5888-419: The mix, are being tested and used. These developments are ever growing in relevance to minimize the impacts caused by cement use, notorious for being one of the largest producers (at about 5 to 10%) of global greenhouse gas emissions . The use of alternative materials also is capable of lowering costs, improving concrete properties, and recycling wastes, the latest being relevant for circular economy aspects of

5980-478: The mixed concrete, often to a concrete mixer truck. Modern concrete is usually prepared as a viscous fluid, so that it may be poured into forms. The forms are containers that define the desired shape. Concrete formwork can be prepared in several ways, such as slip forming and steel plate construction . Alternatively, concrete can be mixed into dryer, non-fluid forms and used in factory settings to manufacture precast concrete products. Interruption in pouring

6072-441: The mixing of cement and water into a paste before combining these materials with aggregates can increase the compressive strength of the resulting concrete. The paste is generally mixed in a high-speed , shear-type mixer at a w/c (water to cement ratio) of 0.30 to 0.45 by mass. The cement paste premix may include admixtures such as accelerators or retarders, superplasticizers , pigments , or silica fume . The premixed paste

6164-440: The mixture forms a fluid slurry that is easily poured and molded into shape. The cement reacts with the water through a process called concrete hydration that hardens it over several hours to form a hard matrix that binds the materials together into a durable stone-like material that has many uses. This time allows concrete to not only be cast in forms, but also to have a variety of tooled processes performed. The hydration process

6256-465: The new St Paul's Cathedral was a great boost for the quarries and established Portland as London's choice of building stone. The island was connected by railway to the rest of the country from 1865. Albion Stone PLC has been quarrying and mining Portland stone since 1984. Portland Stone Firms Ltd have been quarrying Portland stone since 1994. Jordans is part of the Inmosthay Quarry in the centre of

6348-790: The new WCEC extension in Portland Roach which was short-listed for the Stirling Prize in 2017, Somerset House (1792), the General Post Office (1829), the Bank of England , the Mansion House and the National Gallery . Tower Bridge is partly clad in Portland stone (along with Cornish granite ). Portland stone was used in 1923 to build the supporting pillar of the Grace Gates at Lord's Cricket Ground . Recently, Portland stone has been used in

6440-428: The past, lime -based cement binders, such as lime putty, were often used but sometimes with other hydraulic cements , (water resistant) such as a calcium aluminate cement or with Portland cement to form Portland cement concrete (named for its visual resemblance to Portland stone ). Many other non-cementitious types of concrete exist with other methods of binding aggregate together, including asphalt concrete with

6532-469: The process to open this mine in 2015 and reserves are estimated to last for 50 years (2066). Independent Quarry and Admiralty Quarry are both owned by The Crown Estate and have been leased since 1982. These quarries have been worked since the mid-19th century with the final dimension stones coming out of Independent in 2006, although some stocks of Portland stone block still remain. Coombefield Quarry , located near Southwell has been open cast quarried over

6624-506: The properties or increase the performance envelope of the mix. Design-mix concrete can have very broad specifications that cannot be met with more basic nominal mixes, but the involvement of the engineer often increases the cost of the concrete mix. Concrete mixes are primarily divided into nominal mix, standard mix and design mix. Nominal mix ratios are given in volume of Cement : Sand : Aggregate {\displaystyle {\text{Cement : Sand : Aggregate}}} . Nominal mixes are

6716-468: The quality and nature of the product. Design mix ratios are decided by an engineer after analyzing the properties of the specific ingredients being used. Instead of using a 'nominal mix' of 1 part cement, 2 parts sand, and 4 parts aggregate (the second example from above), a civil engineer will custom-design a concrete mix to exactly meet the requirements of the site and conditions, setting material ratios and often designing an admixture package to fine-tune

6808-476: The quarries' environmental performance and removed the potential for any possible damage to the stone being quarried through shock. Full account of the local jointing pattern is made when deciding the position and orientation of cuts. Once the quarry faces have been cut, the stone is gently displaced hydraulically. This is done using "hydro-bags", which are thin, flat, steel bags or envelopes that when inflated with water under moderate pressure, are capable of producing

6900-493: The refurbishment of the British Museum 's central court, the planned Portland stone was controversially substituted with Anstrude Roche Claire stone from France, another similar (but cheaper) oolitic limestone. The term, "Portland cement", was coined by Joseph Aspdin who in 1824 patented a hydraulic binder created by burning a mixture of limestone and clay , resembling the previously existing Roman cement and presenting

6992-485: The rock from its natural bed, hopefully undamaged. Stone was cut using plugs and feathers , where a series of short, small diameter (typically 30 mm) holes are drilled in a line where a cut is to be made. One plug and two feathers were inserted into each hole and each plug is hit in turn with a sledgehammer until the stone yields to the extreme tensile stresses produced. Most stone is many times weaker in tension than in compression, plugs and feathers utilise this fact. It

7084-632: The royal palace of Tiryns , Greece, which dates roughly to 1400 to 1200 BC. Lime mortars were used in Greece, such as in Crete and Cyprus, in 800 BC. The Assyrian Jerwan Aqueduct (688 BC) made use of waterproof concrete . Concrete was used for construction in many ancient structures. Mayan concrete at the ruins of Uxmal (AD 850–925) is referenced in Incidents of Travel in the Yucatán by John L. Stephens . "The roof

7176-494: The sea allowed the quarried stone blocks to be moved over relatively large distances by barge. Portland stone was used to build the Palace of Westminster in 1347, the Tower of London in 1349 and the first stone London Bridge in 1350. Exeter Cathedral and Christchurch Priory , also constructed during the 14th Century, are built of Portland stone. Its superb characteristics have ensured

7268-484: The sea floor. Small particles of sand or organic detritus, such as shell fragments, formed a nucleus, which became coated with layers of calcite as they were rolled around in the muddy micrite. Portland stone measures 3.5 on the Mohs scale of mineral hardness . The calcite gradually accumulated (by accretion) around the fragments of shell in concentric layers, forming small balls (of less than 0.5 mm diameter). This process

7360-482: The southern tip of the island has permission to be worked by Portland Stone Firms and will provide in excess of 30 years of reserves. Permission has been granted for this to be open cast quarried. Once quarries have been worked they are then restored. The Portland Sculpture and Quarry Trust was formed in 1983 and is dedicated to preserving a knowledge and understanding of stone and the landscape from which it comes. The main non-working quarry remains Tout Quarry in which

7452-490: The stone is sufficiently well cemented to allow it to resist weathering, but not so well cemented that it cannot be readily worked (cut and carved) by masons. This is one of the reasons why Portland stone is so favoured as a monumental and architectural stone. Geoff Townson conducted three years doctoral research on the Portlandian, being the first to describe the patch-reef facies and Dorset-wide sedimentation details. Ian West of

7544-494: The stone using mining rather than quarrying techniques. The reserves to the north will be quarried using the diamond bladed cutting machines, hydro bags and wire saws to shape the blocks. This process avoids the use of dusty and noisy blasting as the primary extraction method, thereby protecting the surrounding environment, which has been designated as a Site of Special Scientific Interest (SSSI). Albion Stone PLC now extract all their stone through mining which dramatically reduces

7636-411: The strength of the concrete bonding to resist tension. The long-term durability of Roman concrete structures has been found to be due to its use of pyroclastic (volcanic) rock and ash, whereby the crystallization of strätlingite (a specific and complex calcium aluminosilicate hydrate) and the coalescence of this and similar calcium–aluminium-silicate–hydrate cementing binders helped give the concrete

7728-497: The surface of concrete for a decorative "exposed aggregate" finish, popular among landscape designers. Admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. Admixtures are defined as additions "made as the concrete mix is being prepared". The most common admixtures are retarders and accelerators. In normal use, admixture dosages are less than 5% by mass of cement and are added to

7820-535: The surfaces of the aggregate together, and is typically the most expensive component. Thus, variation in sizes of the aggregate reduces the cost of concrete. The aggregate is nearly always stronger than the binder, so its use does not negatively affect the strength of the concrete. Redistribution of aggregates after compaction often creates non-homogeneity due to the influence of vibration. This can lead to strength gradients. Decorative stones such as quartzite , small river stones or crushed glass are sometimes added to

7912-482: The trust is based, where a workshop is held every year. Tout Quarry has been donated to the Portland Sculpture and Quarry Trust by Portland Stone Firms Limited. Traditionally small diameter holes (35 mm) were drilled horizontally under each rock and charged with a small quantity of gunpowder , chosen because of its relative non-shattering properties. When fired the gunpowder produced a "heave" which dislodged

8004-655: The various ingredients used to produce a given quantity of concrete, the cement is the most energetically expensive. Even complex and efficient kilns require 3.3 to 3.6 gigajoules of energy to produce a ton of clinker and then grind it into cement . Many kilns can be fueled with difficult-to-dispose-of wastes, the most common being used tires. The extremely high temperatures and long periods of time at those temperatures allows cement kilns to efficiently and completely burn even difficult-to-use fuels. The five major compounds of calcium silicates and aluminates comprising Portland cement range from 5 to 50% in weight. Combining water with

8096-439: The water content or adding chemical admixtures increases concrete workability. Excessive water leads to increased bleeding or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. Changes in gradation can also affect workability of the concrete, although a wide range of gradation can be used for various applications. An undesirable gradation can mean using

8188-515: Was Smeaton's Tower , built by British engineer John Smeaton in Devon , England, between 1756 and 1759. This third Eddystone Lighthouse pioneered the use of hydraulic lime in concrete, using pebbles and powdered brick as aggregate. A method for producing Portland cement was developed in England and patented by Joseph Aspdin in 1824. Aspdin chose the name for its similarity to Portland stone , which

8280-602: Was greatly reduced. Low kiln temperatures in the burning of lime, lack of pozzolana, and poor mixing all contributed to a decline in the quality of concrete and mortar. From the 11th century, the increased use of stone in church and castle construction led to an increased demand for mortar. Quality began to improve in the 12th century through better grinding and sieving. Medieval lime mortars and concretes were non-hydraulic and were used for binding masonry, "hearting" (binding rubble masonry cores) and foundations. Bartholomaeus Anglicus in his De proprietatibus rerum (1240) describes

8372-520: Was quarried on the Isle of Portland in Dorset , England. His son William continued developments into the 1840s, earning him recognition for the development of "modern" Portland cement. Reinforced concrete was invented in 1849 by Joseph Monier . and the first reinforced concrete house was built by François Coignet in 1853. The first concrete reinforced bridge was designed and built by Joseph Monier in 1875. Prestressed concrete and post-tensioned concrete were pioneered by Eugène Freyssinet ,

8464-584: Was used for the Armed Forces Memorial in Staffordshire , England. Designed by Liam O'Connor Architects and Planning Consultants, it was completed in 2007 at a cost of over £6 million and bears the names of over 16,000 service personnel of the British Armed Forces killed since the Second World War. Portland stone is recognised to be of a high quality, but is somewhat expensive. In the case of

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